Known in the art is an internal combustion engine in which an exhaust purification catalyst is arranged in an engine exhaust passage and a hydrocarbon feed valve is arranged upstream of the exhaust purification catalyst in the engine exhaust passage, the exhaust purification catalyst has the property of reducing the NOx which is contained in exhaust gas if making a concentration of hydrocarbons which flow into the exhaust purification catalyst vibrate by within a predetermined range of amplitude and by within a predetermined range of period and has the property of being increased in storage amount of NOX which is contained in the exhaust gas if making the vibration period of the hydrocarbon concentration longer than the predetermined range, a first NOx removal method which injects hydrocarbons from the hydrocarbon feed valve by a predetermined injection period to thereby remove the NOx which is contained in the exhaust gas and a second NOx removal method which makes the air-fuel ratio of the exhaust gas which flows into the exhaust purification catalyst rich to make the exhaust purification catalyst release the stored NOx when the NOx which is stored in the exhaust purification catalyst exceeds the allowable value are selectively used, and in the second NOx removal method, the period by which the air-fuel ratio of the exhaust gas which flows into the exhaust purification catalyst is made rich is longer than the above-mentioned predetermined injection period (for example, see Patent Literature 1).
In this internal combustion engine, when the temperature of the exhaust purification catalyst is high, the NOx removal action by the first NOx removal method is performed, while when the temperature of the exhaust purification catalyst is low, the NOx removal action by the second NOx removal method is performed. In this regard, in this internal combustion engine, when the NOx removal action by the first NOx removal method is being performed, the exhaust purification catalyst stores NOx. If the amount of NOx which is stored in this exhaust purification catalyst increases, the NOx removal rate at the time when the NOx removal action by the first NOx removal method is being performed ends up falling. Therefore, in this internal combustion engine, when the NOx removal action by the first NOx removal method is being performed, when the NOx which is stored in the exhaust purification catalyst increases, the amount of injection of hydrocarbons from the hydrocarbon feed valve is increased to make the air-fuel ratio of the exhaust gas which flows into the exhaust purification catalyst rich and thereby make the exhaust purification catalyst release the stored NOx.